An intelligent network (IN) is a network architecture to be linked to a basic network (a fixed network or a mobile communication network, for example) and in which the control of services has been transferred from the telephone exchange to a separate intelligent network functional unit, hereinafter called a service control point (SCP). This makes the services independent of the operation of the basic network, and the structure and software of the basic network do not have to be changed when services are modified or added. Network nodes attending to an intelligent network interface are called service switching points (SSP). Typically, an SSP is a network node responsible for connection set-up, the exchange of the basic network, for example. Hereinafter the services produced by an intelligent network will be called intelligent services.
When a call to which an intelligent service is related is set up, the service switching point SSP attends to the set-up arrangements. In response to the fulfilment of a given authentication condition (i.e., a given call-related event), the service switching point triggers the intelligent service by sending a service request to the control point. At the same time, the SSP interrupts the processing of the call and waits for an instruction/instructions from the SCP. When an intelligent service is triggered, a service logic program SLP is initiated in the service control point SCP and the operation of the program determines the instructions the SCP will send to the SSP at different stages of a call.
Since one service control point SCP can receive service requests from several switching points, and several requests from one switching point, the service switching point that sent the request cannot know how loaded the control point is. Protocols based on the INAP (Intelligent Network Application Protocol), such as CoreINAP and fixed INAP used in fixed networks and mobileINAP used in mobile communication networks, comprise a non-call-associated operation by which the control point can restrict the number of intelligent network service requests sent by the switching point. The control point sends this operation to the switching point when overloading is detected in the control point irrespective of whether the switching point is sending a service request to the control point or not.
Protocols, which take into account the special requirements of a mobile communication system, have been developed for mobile communication networks. An example of such a protocol is the CAP protocol (CAMEL Application Protocol) used by the pan-European GSM system (Global System for Mobile communications) in intelligent services. CAMEL (Customized Applications for Mobile network Enhanced Logic) is one of the GSM phase 2+ services. The CAMEL phase 1 and phase 2 standards do not describe how to operate when a control point is overloaded. The CAMEL phase 1 and 2 CAP protocols do not even define an operation by which the control point could restrict the number of intelligent service requests.